Polycarboxy-triphenyl phosphates

ABSTRACT

Polycarboxy-triphenyl phosphates are prepared by oxidizing corresponding polymethyltriphenyl phosphates. They are fire resistant and stable, and are useful not only as fire-retarding agents for high polymer materials but also as intermediates for various synthetic products. When these esters and hydrolyzed, corresponding aromatic hydroxycarboxylic acids can be obtained with advantages.   WHEREIN N1, N2 AND N3 ARE INDIVIDUALLY ZERO OR AN INTEGER OF UP TO 2, AND N1 + N2 + N3 IS 2 OR MORE; M1, M2 AND M3 ARE INDIVIDUALLY ZERO OR AN INTEGER OF UP TO 2, AND N1 + M1, N2 + M2 AND N3 + M3 DO INDIVIDUALLY NOT EXCEED 3; AND THE SUBSTITUTED POSITIONS OF THE CARBOXYL GROUPS ARE IN THE 3-, 4- OR 5-POSITIONS OF THE INDIVIDUAL PHENYL GROUPS.

United States atent Ito et al. y 30, 1972 [54] POLYCARBOXY-TRIPHENYL[57] ABSTRACT PHOSPHATES Polycarboxy-triphenyl phosphates are preparedby oxidizing [72] Inventors: Ken Ito; Hlroshi Kaminaka, both ofcorresponding P y y p y p p y are fire Toyonaka-shi; Norio Kotera,Amagasakishi; Hiroshi Kuruma, Toyonaka-shi; Yoshiro Murata, Minoo-shi,all of Japan [73] Assignee: Sumltomo Chemical Company, Ltd.,

Osaka, Japan [22] Filed: Sept. 2, 1969 [21] Appl. No.: 854,729

[30] Foreign Application Priority Data Sept. 19, 1968 Japan ..43/68097Feb. 26, 1969 Japan ..44/14945 [52] US. Cl ..260/942, 260/521, 260/968,260/983 [5 1] Int. Cl ..C07f 9/08, C07f9/12 [58] Field of Search..260/942, 968, 983

[56] References Cited FOREIGN PATENTS OR APPLICATIONS 1,122,521 l/l962Germany ..260/942 Primary Examiner-Joseph Rebold AssistantExaminer-Richard L. Raymond Attorney-Stevens, Davis, Miller & Mosherresistant and stable, and are useful not only as fire-retarding agentsfor high polymer materials but also as intermediates for varioussynthetic products. When these esters and hydrolyzed, correspondingaromatic hydroxycarboxylic acids can be obtained with advantages.

The polycarboxy-triphenyl phosphates have the formula:

(COOH)n (HO 0 0 n 0 O P/ 9 2 ll 000mm 1: 0pm 0- wherein n n-; and n, areindividually zero or an integer of up to 2, and n +n +n is 2 or more; mm and m are individually zero or an integer of up to 2, and n +m n +mand n m do individually not exceed 3; and the substituted positions ofthe carboxyl groups are in the 3-, 4- or S-positions 0f the individualphenyl groups.

9 Claims, No Drawings POLYCARBOXY-TRIPHENYL PHOSPHATES This inventionrelates to novel polycarboxy-triphenyl phosphates and to a process forpreparing aromatic hydroxycarboxylic acids therefrom.

The novel polycarboxy-triphenyl phosphates, which are provided inaccordance with the present invention, are represented by the formula,

(HO O C)n 01mm. COOH)n o\ 3 113cm 0- 011mm (I) wherein n,, n and n areindividually zero or an integer of up to 2, and n n n is 2 or more; m mand m are individually zero or an integer of up to 2, and n m n m and nm do individually not exceed 3; and the substituted positions of thecarboxyl groups are selected from the 3-, 4- and 5- positions ofindividual phenol groups. (The novel polycarboxy-triphenyl phosphateswill be referred to as T??- polycarboxylic acids, hereinafter.)

The TPP-polycarboxylic acids of the present invention are aromaticpolycarboxylic acids having phosphate ester bonds in the molecules, andare novel compounds which have never been disclosed in the knownliterature. The TPP-polycarboxylic acids have many such excellentproperties, e.g. they are high in melting point, in general, stable toheat, difficultly inflammable and self-extinguishable, and the phosphateester bonds in the molecules thereof are also relatively stable tohydrolysis. By virtue of these excellent properties, the TH-polycarboxylic acids are particularly suitable as constituents ofsynthetic resins, synthetic fibers and other high polymer substances,which are required to be heat resistant and fire resistant, and asvarious processing agents for imparting fire resistance or flameresistance to common synthetic resins, natural and synthetic fibers,etc. i

The TPP-polycarboxylic acids are also valuable as intermediates foraromatic carboxylic acids, and it has been found that when they arehydrolyzed, hydroxyphenyl carboxylic acids can be obtained withadvantages.

The TPP-polycarboxylic acids represented by the formula (I) are preparedby oxidizing corresponding polymethyltriphenyl phosphates.

As to the oxidation of esters of alkylphenols with molecular oxygen,nothing has heretofore been known except the oxidation of acetate estersof cresol. Tolyl acetate can be easily synthesized and one which is highin purity is readily obtainable. On the other hand, however, the tolylacetate is not sufficient in resistance to hydrolysis during oxidationreaction, and has the drawback that a part thereof is hydrolyzed withwater formed during the reaction to give a free phenolic compound, whichfrequently disturb the progress of reaction. Accordingly, the oxidationthereof must to be discontinued at a low conversion, or variouscountermeasures should be taken so as not to cause the stoppage ofreaction.

Noticing the stability of esters of aromatic phosphoric acids, thepresent inventors made various studies to find that methyl groups linkedto the aromatic nuclei of esters of aromatic phosphoric acids easilyundergo oxidation, but ester bonds linked to phosphoric acids arerelatively stable to hydrolysis under oxidation conditions and thereoccurs no such hydrolysis as to disturb the oxidation.

The present invention has been developed on the basis of theabove-mentioned new finding.

It is therefore the objects of the present invention to provide noveland useful TPP-polycarboxylic acids formed by oxidation of methylphenylphosphates, and to provide a novel process for preparing aromatichydroxycarboxylic acids by hydrolyzing said TPP-polycarboxylic acids.

In accordance with the present invention, the TPP-polycarboxylic acidsrepresented by the formula (I) are prepared by oxidizingpolymethyl-triphenyl phosphates of the formula,

( zl z HCl (2)1 wherein l 1 and 1 are individually zero or an integer ofup to 3, and 1 1 1 is 2 or more; and at least 2 of the methyl groupshave been substituted in the 3-, 4- or 5 -positions of the phenylgroups.

Further, in accordance with the present invention, various aromatichydroxycarboxylic acids are prepared by the hydrolysis of theTPP-polycarboxylic acids of the formula (I).

Examples of the TPP-polycarboxylic acids provided according to thepresent invention include:

3 ,3 ,3 -Tricarboxy-triphenyl phosphate,

4,4 ,4 '-Trica.rboxy-triphenyl phosphate,

3 ,3 ,4 -Tricarboxy-triphenyl phosphate,

3 ,4 ,4 -Tricarboxy-triphenyl phosphate,

2-Methyl-3 ,3 -dicarboxy-triphenyl phosphate,

2-Methyl-3',4-dicarboxy-triphenyl phosphate,

2-Methyl-4 ,4 '-dicarboxy-triphenyl phosphate,

3-Methyl-3',3"-dicarboxy-triphenyl phosphate,

3-Methyl-3 ,4 -dicarboxy-triphenyl phosphate,

3-Methyl-4 ,4-dicarboxy-triphenyl phosphate,

4-Methyl-3,3 '-dicarboxy-triphenyl phosphate,

4-Methyl-3 ,4 '-dicarboxy-triphenyl phosphate 4-Methyl-4' ,4-dicarboxy-triphenyl phosphate,

3,3-DicarboXy-triphenyl phosphate,

3,4-Dicarboxy-triphenyl phosphate, 4,4-Dicarboxy-triphenyl phosphate2,2,2"-Trimethyl-3,3,3"-tricarboxy-triphenyl phosphate,

2,2 ,2 3-Tetramethyl-3 ,3 '-dicarboxy-triphenyl phosphate,

2,2 ,2 '-Trimethyl-4,4 ,4 -tricarboxy-triphenyl phosphate,

2,2 ,2 -4-Tetramethyl-4' ,4 '-dicarboxy-triphenyl phosphate,

2,2 ,2 -Tn'methyl-5 ,5 ,5 '-tricarboxy-triphenyl phosphate,

2,2 ,2 ,S-Tetramethyl-S ,5 -dicarboxy-triphenyl phosphate,

3,3 ,3 ,4,4 ,4 -Hexacarboxy-triphenyl phosphate,

3-Methyl-3 ,3 ,4,4 ,4 '-pentacarboxy-triphenyl phosphate,

3 ,3 '-Dimethyl-3 ,4,4 ,4 -tetracarboxy-triphenyl phosphate,

3 ,3 ,3 '-Trimethyl-4,4 ,4 '-tricarboxy-triphenyl phosphate,

3 ,3 ,3 ,4-Tetramethyl-4 ,4 -dicarboxy-triphenyl phosphate,

3,3,3",5,5,5"-Hexacarboxy-triphenyl phosphate,

3-Methyl-3',3,5,5',5"-pentacarboxy-triphenyl phosphate,

3 ,3-Dimethyl-3' ,5,5 ,5 -tetracarboxy-triphenyl phosphate,

3 ,3 ,3 -Trimethyl-5 ,5 ,5 '-tricarboxy-triphenyl phosphate,

3,3 ,3 ,S-Tetramethyl-S ,5 '-dicarboxy-triphenyl phosphate,

2,2-Dimethyl-3 ,3 '-dicarboxy-triphenyl phosphate,

2,2-Dimethyl-4,4-dicarboxy-triphenyl phosphate2,2-Dimethyl-5,5-dicarboxy-triphenyl phosphate 3 ,3 ,4,4'-Tetracarboxy-triphenyl phosphate,

3-Methyl-3 ,4,4-tricarboxy-triphenyl phosphate,

3,3'-dimethyl-4,4'-dicarboxy-triphenyl phosphate,

3 ,3 ,5 ,5 -Tetracarboxy-triphenyl phosphate,

3-Methyl-3 ,5 ,5 -tricarboxy-triphenyl phosphate,

3,3-Dimethyl-5,5'-dicarboxy-triphenyl phosphate,

3 ,S-dicarboxy-tn'phenyl phosphate,

2,2,2,6,6',6"-Hexamethyl-4,4,4"-tricarboxy-triphenyl phosphate,

2,2 ,4 ,4 ,6,6 ,6 -Heptamethyl-4,4-dicarboxy-triphenyl phosphate,

2,2 ,2 '-Trimethyl-3 ,3 -dicarboxy-triphenyl phosphate,

2,2 ,2" -Trimethyl-4,4' -dicarboxy-triphenyl phosphate,

2,2 ,2 '-Trimethyl-5 ,5 -dicarboxy-triphenyl phosphate,

2-Methyl-3 ,3 ,4' ,4 -tetracarboxy-triphenyl phosphate,

2,3 -Dimethyl-3 ,4 ,4 -tricarboxy-triphenyl phosphate,

2,3 ,3 -Trimethyl-4' ,4 -tricarboxy-triphenyl phosphate,

2-Methyl-3 ,3 ,5 ,5 '-tetraca.rboxy-triphenyl phosphate,

2,3 '-Dimethyl-3 ,5 ,5 '-tricarboxy-triphenyl phosphate,

2,3 ,3 -Trirnethyl-5' ,5 -dicarboxy-triphenyl phosphate,

2,2 '-Dimethyl-3,3 ,3 '-tricarboxy-triphenyl phosphate,

2,2 ,3-Trimethyl- 3 ,3 -dicarboxy-triphenyl phosphate,

2,2 ,3 '-Trimethyl-3 ,3 -dicarboxy-triphenyl phosphate,

2,2-Dimethyl-3",4,4'-tricarboxy-triphenyl phosphate,

2,2 ,3 -Trimethyl-4,4'-dicarboxy-triphenyl phosphate,

2,2 ,4-Trimethyl-3 ,4-dicarboxy-triphenyl phosphate,

2,2 -Dimethyl-3 ,5 ,5 -trica.rboxy-triphenyl phosphate,

2,2 ,3 -Trimethyl-5 ,5 '-dicarboxy-triphenyl phosphate,

2,2 ,5-Trimethyl-3 ,5 '-dicarboxy-triphenyl phosphate,

3 ,3 ,3 ,4,4'-Pentacarboxy-triphenyl phosphate,

3-Methyl-3 ,3 ,4,4'-Tetracarboxy-triphenyl phosphate,

3-Methyl-3 ,3 ,4' ,4 '-tetrac arboxy-triphenyl phosphate,

3 ,3 -Dimethyl-3 ,4,4'-tricarboxytriphenyl phosphate,

3 ,3 '-Dimethyl-3 ,4,4 '-tricarboxy-triphenyl phosphate,

3 ,3 ,3 '-trimethyl-4,4'-dicarboxy-triphenyl phosphate,

3,3,4-trimethyl-3 ,4-dicarboxy-triphenyl phosphate,

3 ,3 ,3 ,5 ,5 '-Pentacarboxy-triphenyl phosphate,

3-Methyl-3 ,3 ,5 ,5 -tetracarboxy-triphenyl phosphate,

3-Methyl3 ,3 ,5 ,5 '-tetracarboxy-triphenyl phosphate,

3,3-dimethyl-3",5,5'-tricarboxy-triphenyl phosphate,

3,3'-Dimethyl-3",5,5-tricarboxy-triphenyl phosphate,

3,5-Dimethyl-3 ,3",5-tricarboxy-triphenyl phosphate,

3,3 ,3 '-Trimethyl-5 ,5 '-dicarboxy-triphenyl phosphate,

3,3',5Trimethyl-3",5-dicarboxy-triphenyl phosphate,

2,2'-Dimethyl-3",5"-dicarboxy-triphenyl phosphate,

3 ,3 ,3 ,5 -tetracarboxy-triphenyl phosphate,

3-Methyl-3 ,3 ,S-tricarboxy-triphenyl phosphate,

3-Methyl-3 ,3 ,5 -tricarboxy-triphenyl phosphate,

3 ,3 -Dimethyl-3 ,5 -dicarboxy-triphenyl phosphate,

3 ,5-Dimethyl-3 ,3 '-dicarboxy-triphenyl phosphate,

3,3 -Dimethyl3 ,5"-dicarboxy-triphenyl phosphate,

3,3 ,5-Tricarboxy-triphenyl phosphate,

3-Methyl-3',5-dicarboxy-triphenyl phosphate,

3-Methyl-3 ,5-dicarboxy-triphenyl phosphate,

2,6-Dimethyl-3,3"-dicurboxy-triphenyl phosphate,

2.2',2".6-Tctramethyl-4',5-dicarboxy-triphenyl phosphate, andsubstituted isomers and mixtures thereof.

These TPP-polycarboxylic acids can be prepared by oxidizingcorresponding polymethyl-triphenyl phosphates. For example, when tri(m-tolyl) phosphate is oxidized, 3,3',3"- tricarboxy-triphenyl phosphateis chiefly obtained. Further, when his (3,4-xylyl) monophenyl phosphateis oxidized, there is obtained a mixture comprising dicarboxylic acidssuch as 3,3-dimethyl-4,4'-dicarboxy-triphenyl phosphate, tricarboxylicacids such as 3-methyl-3,4,4'-tricarboxy-triphenyl phosphate, andtetracarboxylic acids such as 3,3,4,4- tetracarboxy-triphenyl phosphate.If necessary, the mixture can be separated into individual components.

When the TPP-polycarboxylic acids of the formula (I) are hydrolyzed,corresponding aromatic hydroxycarboxylic acids are obtained. Generally,aromatic hydroxycarboxylic acids are important compounds as startingmaterials and intermediates for production of synthetic fibers,synthetic resins, synthetic dyes, medicines, agricultural chemicals,high polymerprocessing agents, etc. Among these, some compounds havealready been prepared on commercial scale and have been used inlargequantities. On the other hand, not a few of them have not yet beenutilized widely, despite the fact that their usefulness has beenconfirmed, because no synthesis process suitable for commercial scaleproduction thereof has been established.

The aromatic hydroxycarboxylic acids obtained according to the presentprocess are those corresponding to the structures of TPP-polycarboxylicacids of the formula (I), and represented by the formulas,

(HOOC m I -OH, -OH and/or (H C)m llmna (COOl-Dm wherein m,, m m;,, 21,,n and n are as defined previously.

It is needless to say that the polymethyl-triphenyl phosphates employedas starting materials in the present invention should have suchstructures that the carboxyl groups of the desired TPP-polycarboxylicacids have been replaced by methyl groups. For example, in order toobtain 4,4,4"- tricarboxy-triphenyl phosphate, it is necessary to usetri (ptolyl) phosphate as the starting material. Methyl groups, whichhave been substituted in the orthopositions, i.e. the 2- or -position,are extremely slow in rate of oxidation, and there are some cases wherethey can be regarded as being substantially not oxidized. Accordingly,the starting polymethyltriphenyl phosphates should be those which haveat least two methyl groups in the 3-, 4- or 5-position of the threephenyl groups. (Hereinafter, the methyl groups in the 3-, 4- or5-position will sometimes be referred to as oxidizable methyl groups" soas to be distinguishable from those in the 2- or 6- position.)

A general process for synthesizing phenyl phosphate esters andderivatives thereof is well known. It is also well known that some ofsaid esters and derivatives are produced in large quantities oncommercial scale and are supplied at economical costs to variousapplication fields. From such commercially available triphenyl phosphateester derivatives, those which conform to the object of the inventionmay be selected. For example, a phosphate ester, which is sold under thetrade name Tricresyl Phosphate (TCP), is ordinarily synthesized byreacting a tar-acid fraction called metacresilic acid with phosphorusoxychloride, and has widely been used as plasticizers, fire retardantsand petroleum additives. In the case of such commercially available TCP,the tar-acid, which is a starting material for the synthesis thereof,usually contains many kinds of components such asphenol and isomers ofxylenol, and other alkylphenols, in addition to 3 kinds of cresolisomers. Accordingly, TCP itself, which is synthesized from thetar-acid, is extremely complex in composition, in most cases. Even suchTCP may be used as the starting material in the present invention, aslong as at least 2 oxidizable methyl groups are substantially present inone molecule. It is, however, needless to say that in the above case,the resulting TPP-polycarboxylic acid and aromatic hydroxycarboxylicacid obtained by hydrolyzing the same are mixtures, which are complex incomposition resulting from to the compositions of the startingmaterials.

In order to obtain TPP-polycarboxylic acids specific in structure, it isnecessary to use, as the starting materials, polymethyl-triphenylphosphates which correspond thereto in structure. The synthesis ofpolymethyl-triphenyl phosphates having such specific structurescan alsobe effected easily according to a known process. For example, about 3moles of mcresol is allowed to react with 1 mole of phosphorusoxychloride in the presence of aluminum chloride as a catalyst to obtain3,3 ,3 '-trimethyl-triphenyl phosphate, which is used as a startingmaterial for 3-methyl-3,3"-dicarboxy-triphenyl phosphate and/or3,3',3"-tricarboxy-triphenyl phosphate. Further, for the preparation of4,4-dimethyltriphenyl phosphate, there is adopted a 2-stage reactionprocess, in which about 1 mole of phenol is allowed to react with 1 moleof phosphorus oxychloride and the resulting (mono)phenylphosphoric aciddichloride is reacted, if necessary after purification by rectificationor the like operation, with about 2 moles of p-cresol. The order ofstages in the above process may be reversed. Likewise, phenyl p-tolyl2,4-xylyl phosphate etc. can be synthesized according to a 3-stageprocess.

It is, of course, possible to synthesize a mixture of specificpolymethyl-triphenyl phosphates. For example, about 3 moles of a mixtureof mand p-cresol isomers is allowed to react with 1 mole of phosphorusoxychloride to give a mixture comprising 3,3',3"-trimethyl-triphenylphosphate, 3,3,4"-trimethyltriphenyl phosphate,3,4',4"-tri:nethyl-triphenyl phosphate and 4,4 ,4 -trimethyl-triphenylphosphate.

The polymethyl-triphenyl phosphates obtained in the above-mentionedmanner are subjected to oxidation reaction, whereby part or all of theoxidizable methyl groups thereof are converted to carboxyl groups. Thestarting polymethyltriphenyl phosphates, which are fed to oxidationreaction systems, are desirably those containing not more than 0.1percent of free phenolic compounds.

The free phenolic compounds can be easily removed according to a knownprocedure such as washing with aqueous alkali solution, distillation orthe like.

The oxidation of polymethyl-triphenyl phosphates can be effected by useof such oxidizing agents as molecular oxygen, organic and inorganicperoxides, permanganate, bichromate, nitric acid, ozone, halogens,halogeno-acids, etc. However, in the oxidation of this kind ofcompounds, which have phosphate ester bonds in the molecules, theinfluence of hydrolysis is inevitably brought about to lower the yieldsof TPP-carboxylic acids, if they are contacted with water for a longperiod of time under strongly acidic, strongly basic, elevatedtemperature or the like severe conditions, though the ester bondsthereof are relatively stable to hydrolysis. In order to overcome suchdifficulty, there may be adopted a process, in which said compounds aretreated with the oxidizing agents in a non-aqueous solvent. For example,a process, in which the compounds are treated in pyridine withpermanganates as OX- 5 idizing agents, is recommendable. It is alsoeffective to remove, according to a suitable procedure, water formed dueto oxidation of the methyl groups of said compounds.

For commercial scale oxidation, it is advantageous to use as theoxidizing agent molecular oxygen gas or an oxygen-containing gas such asair. Particularly, the so-called liquid phase air oxidation," in whichthe starting aromatic phosphate esters are oxidized with saidoxygen-containing gas, is one of the most excellent modes of practice ofthe present invention. The 5 oxidation step of the present inventionwill be explained below with respect chiefly to the liquid phase airoxidation.

Molecular oxygen or an oxygen-containing gas such as air, which is usedin the oxidation, should be protected as far as possible fromcontamination by substances which tend to disturb the oxidation orpromote the hydrolysis of said esters, e.g. sulfur compounds, phenolicsubstances, moisture, strong acids and strong alkalis.

Most of the aromatic phosphate esters are relatively stable tohydrolysis. Under severe conditions, however, the influence ofhydrolysis due to contaminating moisture or to water formed during theoxidation reaction is not negligible. It is therefore important toselect such reaction conditions that the rate of hydrolysis issufficiently lower than the rate of oxidation reaction. The reactiontemperature is within the range of from room temperature to 200 C.,preferably from 60 to 150 C. At temperatures above 200 C., the influenceof hydrolysis of the phosphate esters is so great that not only are nofavorable results attained but also stoppage of the oxidation reactionis frequently brought about. The reaction pres- 75 sure isadvantageously atmospheric or an elevated pressure, and is ordinarilywithin the range of from atmospheric pressure to 30 Kg/cm (gauge). Inorder to promote the oxidation reaction, there are used catalystscontaining vanadium, chromium, manganese, cobalt, nickel, copper ormolybdenum. These catalysts are advantageously used in a form capable ofbeing uniformly dissolved or dispersed in the reaction systems. It isalso advantageous for the effective practice of the present invention touse in combination, as cocatalysts and/or promotors, various halidessuch as bromide and the like; organic carbonyl compounds such asacetaldehyde and methylethylketone; various peroxides such as benzoylperoxide and peracetic acid; and ozone.

For the inhibition of hydrolysis, it is a preferable procedure to removewater in the oxidation reaction system. This procedure is particularlyeffective in the case where T??- polycarboxylic acids having a largenumber of carboxyl groups, because in said case, the reaction conditionstend to become severe and the amount of water formed is large. Examplesof dehydration procedures are the addition of a sub stance capable ofco-boiling with water, e.g. benzene; the addition of a substance capableof reacting with water, e.g. acetic anhydride; and the use of asubstance capable of adsorbing water, e. g. molecular sieve.

As the reaction solvent, there is used an inert compound capable ofuniformly dissolving or dispersing the starting aromatic phosphate esterand the catalyst. Preferable solvent is a lower aliphatic carboxylicacid, e.g. acetic, propionic or butyric acid, an anhydride thereof or amixture of these acids.

The reaction time considerably varies depending on the kinds of startingaromatic phosphate ester and on the desired TPP-polycarboxylic acid.However, the reaction conditions should be so chosen that the reactionis substantially complete is a period within the range of from about 4to 24 hours, excluding the induction period. If the reaction time islonger than 24 hours, the influence of hydrolysis and other sidereactions becomes great. When suitable reaction conditions are selected,the reaction can be sufficiently completed within said hours. Theoxidation can be stopped before completion of the reaction. In thiscase, however, unreacted starting aromatic phosphate ester,monocarboxylic acid and other low oxidation degree product are left inlarge amounts to bring about the drawback that the after-stageoperations become complex.

The oxidizability of the methyl groups of polymethyltriphenyl phosphatesgreatly varies depending on the substituted positions thereof. That is,methyl groups, which have been substituted in the 2- and 6-positions ofphenyl groups, are quite difiicultly oxidizable due to their stericconfiguration. In this case, it may be said that no substantialoxidation takes place. In contrast to this, methyl groups, which havebeen substituted in the 3-, 4- and 5-positions of phenyl groups, areeasily oxidizable and are substantially the same in oxidizabiiity.However, in the case of two methyl groups, which have been substitutedin the 3- and 4-positions of same phenyl nucleus, the methyl group inthe 4-position is more easily oxidizable. Accordingly, whentris(2,4-xylyl) phosphate, for example, is oxidized,2,2',2"-trimethyl-4,4',4"-tricarboxytriphenyl phosphate is chieflyformed and, depending on conditions, 2,2 ,2 ,4-tetramethyl-4 ,4'-dicarboxy-triphenyl phosphate is formed in a somewhat large amount,but the amount of 2-carboxy(-substituted) compounds formed is veryslight. In the oxidation of phenylbis-(3,4-xylyl) phosphate, there areformed dicarboxylic and tricarboxylic acids, in addition to3,3',4,4'-tetracarboxy-triphenyl phosphate. However, in the former, i.e.in the dicarboxylic and tricarboxylic acids, methyl groups leftunoxidized are chiefly those in the 3-positions of phenyl groups, andresidual methyl groups in the 4- positions are far less in number.

Procedures for recovering the product TPP-poly-carboxylic acids fromoxidation reaction liquids are more or less different depending on thekind of the carboxylic acids, and therefore the procedures are somewhatindividual in details. Generally, however, the recovery isadvantageously effected in the following manner:

In a few cases where the TPP-polycarboxylic acid formed is relativelydifficultly soluble and can be easily taken out of the reaction mixture,e.g. in case the reaction mixture containing(3,3',3"-tricarboxy)triphenyl phosphate, (4,4',4"-tricarboxy)triphenylphosphate and (3,3',5,5'B-tetracarboxy)triphenyl according to thetreatment of an easily-soluble product. In

case the desired TPP-polycarboxylic acid is easily soluble in solvent orin the case where the product dissolved in the filtrate formed byfiltering ofi" difficultly soluble products, it is general to adopt suchprocedures that the reaction solvent is removed by distillation or thelike means, inorganic residues such as oxidizing agent, catalyst, etc.are removed by such procedure as extraction, precipitation, filtrationor ionexchange, and then the remaining TPP-polycarboxylic acid isseparated and purified. The distillation of solvent and the removal ofinorganics may be effected in the reverse order. If necessary the aboveoperations may be repeated two or more times.

The thus obtained TPP-polycarboxylic acids are white crystals light inweight and are colorless and odorless, in general. In flames, they meltwithout causing decomposition or carbonization. When heated to above 500C., they are gradually decomposed, and the decomposates sometimes causecombustion but the combustion immediately ceases by removal of theflame.

Solubilities of the TPP-polycarboxylic acids for water and variousorganic solvents greatly vary depending on the kind thereof. Generally,the acids are sparingly soluble in cold water and are easily soluble inalcohols such as methanol, ethanol, etc. They are somewhat less solublein acetic acid and ethyl acetate than in alcohols, and are soluble, tosome extent as between said two kinds of solvents, in ketones such asacetone, methylethylketone, etc. They are further low in solubility inaromatic hydrocarbons such as benzene, toluene, etc. and aliphatichydrocarbons such as n-hexane, etc., but most of them are soluble inN,N-dimethylf0rmamide and dimethylsulfoxide.

As is clear from the above explanation, the TPP-polycarboxylic acids canbe prepared with relative ease from starting materials, which areobtainable at low costs and in large quantities, i.e. phosphorusoxychloride and such phenols as phenol, cresol isomers, xylenol isomers,trimethylphenol isomers and mixtures thereof. Moreover, theTPP-polycarboxylic acids have such excellent characteristics as beingdifficultly combustible, stable and heat resistant, and hence aresubstances extremely high in value not only as processing agents forvarious synthetic high polymer substances and various polymersubstances, which are required to be difficultly combustible, flameresistant and heat resistant, e.g. fire-retarding agents, plasticizers,crosslinking agents, water-repelling agents, etc., but also in variouschemical products such as vehicles for paints, surface active agents,additives for lubricating oils, etc.

The novel TPP-polycarboxylic acids thus formed through theabove-mentioned oxidation are subjected, in accordance with the presentprocess, to hydrolysis to give hydroxyphenyl carboxylic acids. That is,the oxidized reaction liquid which has completed the reaction is freedfrom the solvent by distillation and is then subjected to hydrolysis. Ifthe desired oxidation product carboxyphenyl phosphate ester hasdeposited prior to the removal of solvent by distillation, the saidester may be separated by filtration and the hydrolysis treatment may beeffected separately. As the removal of solvent by distillationprogresses, further deposition of product is observed, and therefore,there may be adopted such procedures that the concentration operation isceased at a suitable stage and the precipitate is separated byfiltration. In the filtrate have been concentrated unreacted phosphateester, intermediary oxidation products of phosphate ester (includingpartial oxidation products in which a part of the three to six methylgroups of phosphate ester have converted to carboxyl groups), and moreor less amounts of hydrolyzates and by-products.

The separation and recovery of catalyst may be effected either before orafter the hydrolysis. The catalyst may be separated and recoveredaccording to, for example, any of such procedures that it is recoveredas a reaction solvent-soluble salt; it is dissolved in a mineral acidand is separated; it is formed into a basic and insoluble oxide orhydroxide and is separated by filtration; and it is separated as acomplex salt. Among these, suitable procedures in connection with thehydrolysis step may be effected either independently or in combination.

The hydrolysis is carried out in the presence of mineral acids or basicsubstances. Carboxyphenyl phosphate esters to be fed to the hydrolysisstep include not only high purity esters which have been subjected topurification but also crude esters obtained by filtration and separationfrom oxidation reaction liquids or by removal of solvents therefrom bydistillation. In case a basic substance has been used, it is recovered,after the hydrolysis, by liberating the product according to suchprocedure as acidification or the like. The hydrolysis reaction iseffected at a temperature of 50 to 300 C. under a pressure ofatmospheric to 100 Kg/cm (gauge).

Typical examples of the aromatic hydroxycarboxylic acids obtainableaccording to the present process include, mhydroxybenzoic acid,p-hydroxybenzoic acid, 3-hydroxyphthalic acid, 4-hydroxyphthalic acid,S-hydroxyisophthalic acid, 4-hydroxy-m-toluic acid, 3-hydroxy-p-toluicacid, 3- hydroxy-o-toluic acid, 4-hydroxy-o-toluic acid,S-hydroxy-mtoluic acid, 3,5-dimethyl-p-hydroxybenzoic acid and mixturesthereof.

From the hydrolysis reaction mixture, there are sometimes recovered, inaddition to the said aromatic hydroxycarboxylic acids, more or lessquantities of un oxidized phenolic compounds such as phenol, cresols, orxylenols.

The present invention will be illustrated in detail below, but it isneedless to say that the examples do not limit the scope of theinvention. In the examples, all the units are parts by weight unlessotherwise specified.

EXAMPLE 1 10 Parts of cobaltous acetate (tetraaquo-salt) and 4.4 partsof acetaldehyde were added to 300 parts of glacial acetic acid. Themixture was heated to C. in a cylindrical reactor and was vigorouslystirred for 40 minutes while introducing oxygen gas. By this operation,the mixture was changed in color from the initial reddish purple throughbrown to green, and showed that the cobaltous ion had substantiallyconverted to a cobaltic ion. This mixture was cooled to 70 C. and wascharged with a mixture comprising 41 parts of tri (m-tolyl) phosphateand 49 parts of glacial acetic acid. Subsequently, the mixture wasstirred at 70 75 C. for 9 hours, while introducing oxygen gas. Duringthis period, 0.022 part/min. of acetaldehyde was added to the reactionmixture. After 3 hours from initiation of the reaction, cooling becamenecessary due to generation of heat, and the system was cooled withwater for about 4 hours. At about 4.5th hour after initiation of thereaction, a product began to deposit and, at the 7th hour, unreacted tri(m-tolyl) phosphate completely disappeared. The reaction liquid wascooled to room temperature and was then filtered to obtain 38 parts of acrystal of crude 3,3',3"-tricarboxy-triphenyl phosphate. It was observedthat in the filtrate had been still dissolved, in addition to thecatalyst cobalt salt, small amounts of 3,3',3"-tricarboxy-triphenylphosphate and cobalt salt thereof, and more or less amounts ofby-products and intermediary oxides.

The crude 3,3,3"-tricarboxy-triphenyl phosphate was heated for 1 hourtogether with 3 times the amount thereof of acetic acid to dissolve andremove slight amounts of cobalt and soluble impurities, and was thenrecrystallized from an equal volume mixed solution of ethanol and waterto obtain a white crystal having a melting point of 262 C.

Elementary analysis for C l-l O P: Found: C 55.26%, H 3.30%, Calculated:C 55.03%, H 3.30%,

. EXAMPLE 2 50 Parts of tri(p-tolyl) phosphate and 1 part of manganesenaphthenate were added to a mixed liquid comprising 100 parts of glacialacetic acid and 40 parts of acetic anhydride. Subsequently, the mixturewas oxidized with oxygen at 140 C. under a pressure of 6 Kg/cm (gauge).After an induction period of about 3 hours, the absorption of oxygenbecame vigorous and, after 24 hours, the starting tri(p-tolyl) phosphatewas not left except in a trace amount. The reaction liquid was cooled,and a deposited crystal was separated by filtration to obtain 35 partsof a crude crystal. From the filtrate, acetic acid was removed bydistillation to obtain 30 parts of a residue. The filtration cake wasrecrystallized from waterethanol to obtain 32 parts of a white crystalhaving a melting point of 248 C. The crystal was heated in ethyl acetateto elute small amounts of impurities (this component is referred to ascomponent A) migrated therein, whereby a crystal having a melting pointof 261 .7 262.5 C. was obtained. In the nuclear magnetic resonancespectrum of DMSO-d solution of said crystal, no absorption of unreactedmethyl groups was observed. Further, the elementary analysis values ofsaid crystal were as set forth below. From these results, it was decidedthat said crystal was 4,4,4"-tricarboxytriphenyl phosphate.

Elementary analysis for C H O Pz Found: C 54.89%, Calculated: C 55.03%,

The vaporization residue of the filtrate was heated together withmethylisobutylketone to extract solubles, which were then recrystallizedto obtain 12 parts of a solid having a melting point of about 135 C.This solid was a substantially equal amount mixture of the aforesaidcomponent A and 4,4',4"- tricarboxy-triphenyl phosphate. The former wasseparated according to column chromatography and, for the results of thenuclear magnetic resonance spectrum (in acetone-d solvent) of theremaining substance, it was decided that said substance was4-methyl-4',4"-dicarboxy-triphenyl phosphate. The melting point of thissubstance was 187 C.

EXAMPLE 3 1 Mole of phosphorus oxychloride was allowed to react with 1mole of phenol in the presence of anhydrous aluminum chloride. Theresulting monophenyl dichlorophosphate was separated by distillation andwas then allowed to react with 2 moles of m-cresol, using anhydrousaluminum chloride as a catalyst, to obtain 3,3'-dimethyl-triphenylphosphate. 71 Parts of this phosphate was oxidized for 7 hours in thesame manner as in Example 1, whereby the residual amount of the starting3,3'-dimethyl-triphenyl phosphate became less than 0.1 percent. Thereaction mixture had maintaineda homogeneous phase, and therefore aceticacid was removed by distillation and the residue was dissolved in watertogether with sodium hydrogencarbonate. After heating the solution atabout pH 8 for 10 minutes, a cobalt hydroxide formed was separated byfiltration. To the filtrate was added sulfuric acid, and 65 parts of aliberated organic substance was separated by filtration. This organicsubstance contained, in addition to 3,3'-dicarboxy-triphenyl phosphate,more or less amounts of acetic acid, by-products and intermediaryoxidation products. The organic substance was recrystallized fromwater-ethanol (70 30) and then from a large amount of toluene to obtaina white crystal having a melting point of 142 C.

Elementary analysis for C H O P:

Found: C 58.23%, H 3.61%, P 7.47%

Calculated: C 57.98%, H 3.49%, P 7.48%

The nuclear magnetic resonance spectrum (in CD0 of said crystal showedno presence of unreacted methyl group, and other proton absorptions wellsubstantiated the abovementioned structure. The acid value of thecrystal was 275 (calculated value: 271).

EXAMPLE 4 Elementary analysis for C l-h0 1: Found: C 58.04%, H 3.48%,Calculated: C 57.98%, H 3.49%,

EXAMPLE 5 Tris(3,5-xylyl) phosphate was synthesized from 3,5-xylenol andphosphorus oxychloride. 60 Parts of said phosphate was oxidized withoxygen gas at a temperature of C. in the presence of 15 parts of cobaltacetate and 200 parts of glacial acetic acid. During the oxidation,acetaldehyde as the promoter was intermittently dropped into the systemin a proportion of 2 parts per hour. At about the 3rd hour frominitiation of the reaction, the generation of heat began, and stopped atthe 9th hour. From about this time, the formation of precipitateinitiated. The reaction was ceased at the 12th hour, whereby the amountof unreacted tris(3,5-xyly) phosphate was less than 0.1 percent. Thereaction liquid was cooled and filtered to obtain 32 parts of a crudecake. The filtrate was freed from acetic acid by distillation to obtain70 parts of a residue. The cake was extracted with hot water to removecobalt salt, acetic acid and other impurities, whereby a slightlygreyish white solid was obtained. This solid had a melting point ofabove 250 C.

The solid was dissolved in parts of a 30 percent aqueous caustic sodasolution and was then heated under relux for 20 hours. The reactionliquid was separated by filtration from a slight amount of cobalthydroxide precipitate and was then acidified to pH 1 by addition ofsulfuric acid to deposit a crystal. After cooling the liquid with ice,the crystal was recovered by filtration. The thus obtained crystal was27 parts in amount, and it was found that the crystal was composed of a97 3 mixture of S-hydroxy-isophthalic acid and S-hydroxy-mtoluic acid.This crystal was recrystallized from water to obtain 99.60 percentpurity S-hydroxy-isophthalic acid.

On the other hand, the 70 parts of the vaporization residue of thefiltrate was treated in the same manner as in Example 3 to remove cobaltsalt, whereby 40 parts of a crude organic substance was obtained. Thiscrude organic substance was treated with toluene to remove acetic acid,whereby a yellowish brown solid was obtained. The solid was then heatedunder reflux for 20 hours together with a 30 percent aqueous sodiumhydroxide solution. Thereafter, a cobalt hydroxide formed was removed atan alkaline pH, 2 parts of 3,5-xylenol was extracted and separated at aneutral pH, and 35 parts of a mixture of S-hydroxy-isophthalic acid andS-hydroxy-m-toluic acid was separated by filtration at an acidic pH.This crystal was composed of 75 percent of 5-hydroxy-isophthalic acid,24 percent of 5-hydroxy-mtoluic acid, and 1 percent of other unobviouscomponents.

EXAMPLE 6 100 Parts of tricresyl phosphate prepared from a 61 39 mixtureof m-cresol and p-cresol, 20 parts of cobalt acetate tetra aquo-salt and7 parts of methylethylketone were dissolved in 300 parts of glacialacetic acid, and air was introduced at 1 10 C. for 20 hours. About equalvolume of air to the reaction mixture was introduced every minutes. Inthis case, the reaction system was a homogeneous phase, but the amountof unreacted tricresyl phosphate was not more than about 0.1 percent.After cooling to 50 C., the reaction liquid was charged with 40 parts ofa strongly acidic cation-exchange resin (trade name Amberlyst 15), andwas stirred at said temperature for 100 minutes, whereby the color ofcobalt ion disappeared completely. The resin was separated byfiltration, and the filtrate was mixed with acetic acid, which had beenused for washing the resin. Subsequently, the acetic acid was removed bydistillation from the mixture to obtain 125 parts of a yellow solid.This solid was recrystallized from water-alcohol l 1), whereby 1 18parts of a mixture of tricarboxytriphenyl phosphates was obtained. Thissubstance had a melting point between 180 and 200 C. and showed no clearmelting point. The acid value of said substance was 366 and theelementary analysis values thereof were as set forth below.

Elementary analysis for C H O P: Found: C 55.56%, H 3.41%, Calculated: C55.03%, H 3.30%,

EXAMPLE 7 A mixture comprising 100 parts of diphenyl-Iij-xylylphosphate, 500 parts of glacial acetic acid, 2 parts of cobalt acetateand 70 parts of acetic anhydride was oxidized with oxygen gas at 130 C.under a pressure of 20 Kg/cm After 1 hour from initiation of thereaction, the absorption rate of oxygen became high and, at the 5thhour, said rate became low. During this period, temperature increasetook place due to the heat of oxidation reaction and therefore thesystem was externally cooled, so that the temperature did not exceed 140C.

A homogeneous solution formed after completion of the reaction waspassed through a tower packed with the cationexchange resin Amberlyst15." The eluted solution and the wash liquid of the packed tower weremixed together, and the mixture was concentrated to recover acetic acidand a small amount of acetic anhydride. Subsequently, 120 pans of thedistillation residue was recrystallized from ethyl acetate to obtain 105parts of purified 3,5-dicarboxy-tripheny] phosphate, m.p. 160 C., acidvalue 271 (calculated value 271).

EXAMPLE 8 120 Parts of phenylbis( 3,5xy1yl) phosphate was oxidized at 90C. in the presence of 900 parts of acetic acid and 9 parts of cobaltacetate. During the reaction, 2 parts per hour of acetaldehyde as apromotor and 10 parts per hour of acetic anhydride as a dehydratingagent were added to the system. The reaction was complete in 13 hours,and a precipitate formed was separated by filtration and the filtratewas treated in the same manner as in Example 6. From the precipitate wasobtained by recrystallization 20 parts of a white solid having a meltingpoint of 245.5 C. which was composed essentially of 3,3,5,5trate wasobtained by recrystallization 1 10 parts of a solid having a meltingpoint of 225230 C. which was composed of a mixture of tetracarboxylicacid, tricarboxylic acid and a small amount of dicarboxylic acid.

EXAMPLE 9 Oxidation reaction was effected in the same manner as inExample 2, and the oxidation reaction liquid was cooled to deposit acrystal. This crystal (dry weight 35 parts) was separated by filtration,and the filtrate was freed from acetic acid by distillation to obtain 30parts of a residue. The said crystal and residue were mixed together,and the mixture was heated under reflux for 10 hours together with 200parts of a 30 percent aqueous sodium hydroxide solution. The hydrolysisreaction liquid was filtered to remove manganese hydroxide and was thenadjusted to pH 7 by addition of concentrated hydrochloric acid.Thereafter, the liquid was extracted with ethyl acetate to recover 2parts of p-cresol and more or less amounts of by-products. After theextraction, the aqueous layer was further acidified to pH 1.5, whereby acrystal of phydroxybenzoic acid was deposited. This crystal wasseparated by filtration and was then dried to obtain 49 parts ofp-hydroxybenzoic acid.

EXAMPLE 10 Parts of tricresyl phosphate prepared from a 61 39 mixture ofm-cresol and p-cresol, 20 parts of cobalt acetate (tetraaquo-salt) and 7parts of methylethylketone were dissolved in 300 parts of glacial aceticacid, and air was introduced at C. for 20 hours in a proportion of 601per hour per 1 liter of reaction mixture, whereby the amount of thetricresyl phosphate left in the reaction liquid became about 0.1percent. Subsequently, the solvent was removed by distillation, and theresulting residue was concentrated to parts. This residue was chargedwith 350 parts of 20 percent hydrochloric acid and was then allowed tostand with Stirring in a closed vessel at C. for 20 hours. Thehydrolyzed liquid was cooled and was then filtered to obtain 105 partsof mand p-hydroxybenzoic acids containing a small amount of tarrysubstance. Subsequently, the filtrate was extracted with ethyl acetateto recover 3 parts of mand p-cresols and a more or less amount of aceticacid. In this filtrate, cobalt had been dissolved in the form ofchloride. A portion of the filtrate was vaporized to dryness to findthat the cobalt chloride could be recovered substantiallyquantitatively. The crude hydroxybenzoic acid was recrystallized fromwater-alcohol to obtain 96 parts of a purified product.

EXAMPLE 1 l A mixture comprising 50 parts of tris(m-tolyl) phosphateobtained from m-cresol and phosphorus oxychloride and 30 parts ofglacial acetic acid was added to a mixture prepared in such a mannerthat a mixture composed of 10 parts of cobalt acetate (tetraaquo-salt),200 parts of glacial acetic acid and 3 parts of acetaldehyde wasmaintained at 90 C. and dry air was introduced into the mixture for 40minutes to activate a major proportion of the cobaltous salt to acobaltic salt. Subsequently, the mixture was oxidized at 70 75 C. byintroduction of air. During the oxidation, 2 parts per hour ofacetaldehyde was intermittently dropped into the system. At the 10thhour from initiation of the reaction, the tris(mtolyl)phosphatesubstantially disappeared. A crystal deposited was separated byfiltration from the reaction liquid. From the filtrate, acetic acid wasremoved by filtration until the amount of residual liquid became 100parts. The liquid was allowed to cool and a deposited crystal was againseparated by filtration. A mixture of this crystal and the previouslyseparated crystal, the amount of which was 58 parts, was heated underreflux for 20 hours together with 200 parts of 20 percent hydrochloricacid to effect hydrolysis, whereby 47 parts of m-hydroxybenzoic acid wasobtained. The cobalt-containing second filtrate was further freed bydistillation from acetic acid and was then subjected to hydrolysis at analkaline pH, and cobalt hydroxide was separated by filtration at analkaline pH. The cobalt hydroxide was washed 2 times with water toobtain 7 parts of a hydrated cake. This cake was dissolved in glacialacetic acid, and the solution was used in oxidation of the next time.The hydrolyzed filtrate was neutralized and acidified in the same manneras in Example 9 to recover 1 part of m-cresol and 6 parts ofm-hydroxybenzoic acid.

What is claimed is:

l3 l4 1. An aromatic carboxylic acid represented by the formula and n mdo individually not exceed 3; and the substituted positions of thecarboxyl groups are in the 3-, 4- or 5-positions (C 0mm of individualphenyl groups. (H 0 O C n 0- X 2. 3,3 ,3"-Tricarboxy-triphenylphosphate. (01mm 3. 4,4 ,4 Tricarboxy-triphenyl phosphate. O-P 4.4-Methyl-4' ,4 '-dicarboxy-triphenyl phosphate.

P (C O OHM]: 5. 3,3-Dicarboxy-triphenyl phosphate. (H C)mr 6.4,4'-Dicarboxy-triphenyl phosphate.

(CHmn 7. 3,3,4"-Tricarboxy-triphenyl phosphate.

.s wherein n n and n are individually zero or an integer of up g; zz agr g lt to 2, and n, n n is 2 or more; m,, m and m are inxy'mp eny P 1dividually zero or an integer of up to 2, and n m,, n m a w

2. 3,3'',3''''-Tricarboxy-triphenyl phosphate. 3.4,4'',4''''-Tricarboxy-triphenyl phosphate. 4.4-Methyl-4'',4''''-dicarboxy-triphenyl phosphate. 5.3,3''-Dicarboxy-triphenyl phosphate.
 6. 4,4''-Dicarboxy-triphenylphosphate.
 7. 3,3'',4''''-Tricarboxy-triphenyl phosphate. 8.3,4'',4''''-Tricarboxy-triphenyl phosphate.
 9. 3,5-Dicarboxy-triphenylphosphate.